The present invention relates generally to devices and methods for measuring the position of an object. More particularly, the present invention is useful for measuring the rotational position of a shaft in instruments, such as a joystick or foot pedal, which may transmit off-axis displacements and radial loads into the sensing device. The present invention would be applicable to a variety of endeavors such as computer gaming or robotic control.
Potentiometers and other variable resistors have found widespread use in a variety of electronics-related industries. The computer gaming industry uses these variable resistors and potentiometers to translate hand, foot, and other motions by the user into electrical signal information that a computer can use to interpret the desired actions of the user. For example, during game play, hand movement by the user on an interface such as a joystick may be used to move a cursor on the computer screen for targeting purposes or for on-screen menu item selecting purposes. The accuracy of on-screen cursor movement is directly related to the accuracy of the sensors used in the joystick or user interface. One critical aspect of joystick design is to minimize the amount of movement that the handle must travel before a rotational sensor such as a variable resistor in the joystick registers the movement of the handle. This lag causes imprecise cursor movement that results in poor cursor control on the computer screen. In computer gaming, the greater the lag, the poorer the game play.
Unfortunately, repeated use of the user interface or computer controller such as a joystick or a foot pedal controller, will cause the accuracy of the variable resistors and potentiometers in the device to degrade. As computer gaming enthusiasts probably understand, a computer controller such as a joystick must respond to a variety of sudden and unpredictable movements by the user along a variety of axes. This type of motion may transfer off-axis or radial loads to the sensors used in the computer controller. The low-cost, variable resistors used in computer game controllers are unable to withstand large variations in radial loading and other off-axis forces distributed to the internal mechanisms of the variable resistor during vigorous game play. Additionally, conventional potentiometers and variable resistors are typically rigidly mounted in the computer controllers and end up transferring these loads to the internal mechanisms.
For example, a conventional potentiometer is shown in FIGS. 1A and 1B. Rotation of the shaft S as indicated by arrow 1 changes the resistance of the potentiometer. As shown in FIG. 1B, off-axis forces as indicated by arrows 2 and 4 will cause permanent deformation of the contact wiper W over time, bending the wiper away from the resistive material R even when the shaft S of the variable resister is realigned. The variable resistor functions by having the wiper swipe across the resistive material R to change resistance of the variable resistor based on the rotational position of the wiper. The xe2x80x9clifting offxe2x80x9d of the wiper W will eventually destroy the functionality of the variable resistor as the wiper will no longer be in contact with the resistive material R. With the wiper W lifted away, movement of the shaft is not registered by the variable resistor and, thus the computer does not register the hand or other motions of the user on the controller. Conventional sensors do not have mechanisms for compensating or damping these loads on the sensor, and hence these sensors lack both the robustness and accuracy over time to withstand the rigors of computer game play.
Accordingly, it would be desirable to provide improved rotational position sensors that can compensate for off-axis loads transferred from an attached shaft or object. The ability of these improved sensors to compensate for these loads will increase the functional lifespan of the sensors. Preferably, the improved sensor will be a low-cost part which can be mass-produced using known techniques for use in the computer gaming and computer peripheral industry. The sensor further will allow for ease of assembly and thus increase manufacturing throughput.
The present invention is directed towards devices and methods which can withstand various off-axis displacements and radial forces which degrade the accuracy and life span of conventional rotational position sensors. Specifically, the present invention provides a mounting assembly which reduces the internal bending forces which cause early failure in rotational sensors. A computer peripheral device according to the present invention includes an input shaft attached to a rotational sensor. The mounting assembly coupled to the rotational sensor prevents motion of the sensor body in only one degree of freedom. Preferably, the mounting assembly allows the sensor body to move with the input shaft in five degrees of freedom, thus minimizing bending forces caused when the sensor body is rigidly secured in a fixed position. The ability to move the sensor body in many degrees of freedom allows forces to be transferred through the device, instead of being absorbed by the sensor mechanisms.
In one embodiment, the input shaft and the shaft of the rotational sensor are press-fit together. Advantageously, such a press-fit or interference fit creates a direct-drive connection that improves sensor accuracy by removing slack between a user input and the sensor detecting motion of the user input. Conventionally, such a direct-drive connection would not be possible since it would pass too much bending or off-axis force into the sensor, causing early sensor failure. The mounting assembly of the present invention allows for such a direct-drive connection while preferably increasing life span and accuracy of a rotational sensor.
The input shaft typically forms a connection with a foot pedal or a joystick to receive user input. A protrusion is typically used to connect the sensor body to the mounting assembly and constrain motion of the sensor body in one degree of freedom. Preferably, the mounting assembly prevents rotation of the sensor body about a longitudinal axis of the input shaft. The protrusion, in one embodiment, is otherwise unconstrained by the mounting assembly to move in the channel between two opposing surfaces on the mounting assembly. In other embodiments, the mounting assembly prevents motion of the rotational sensor body in only two degrees of freedom. Optimally, but not necessarily, the rotational sensor will only see those forces required to rotate the shaft of the rotational sensor.
The present invention advantageously improves over conventional sensors that cannot compensate for such loads and exhibited substantially reduced accuracy after extended use. The present invention reduces the effects of these off-axis forces caused by misalignment and manufacturing tolerances associated with mounting of these sensors in various devices. The present invention further reduces the number of moving parts associated with a sensor used for determining the rotational position of an input assembly, thus reducing the overall cost of the device. Simplification of the sensor design and mounting assembly further increases manufacturing throughput of the overall device.
A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.